It is well-known that gear units having oil lubrication are practicable, the oil, i.e., liquid, collecting in the bottom part of the gear-unit interior when the gear unit is not in operation, thus when the gear wheels are stationary, and forming the oil pan there which has an oil level that corresponds to the filling level upon pouring in the oil. During operation of the gear unit, especially at nominal speed of the input shaft and/or output shaft, the gearing parts of the gear unit spray and hurl oil around. In particular, oil is also sprayed out from the gearings engaging with each other. The quantities of oil sprayed around lower the oil level only insignificantly during operation of the gear unit.